Chemically activated methylcyclobutane exothermicity of singlet methylene reactions and the heat of formation of singlet methylene

Abstract

The specific decomposition rates of chemically activated methylcyclobutane produced from CH#Al) reaction with cyclobutane $ave been determined. CHz(lAl)was produced from ketene photolyses at 3340 and 3130 A and from diazomethane photolyses at 4358 and 3660 A. Comparisons of the excitation energies of the methylcyclobutane, determined by RRKM theory calculations, and the experimental results for the ketene systems, with thermochemically predicted maximum excitation energies, favor an Arrhenius A factor in the range of 5 X IOl5 to 1 X 10l6 sec-' for methylcyclobutane. This result is consistent with ( I ) the comparison of RRKM theory calculations and the experimental unimolecular falloff for methylcyclobutane, (2) the comparison of experimental A factors for cyclobutane and other alkylcyclobutane decompositions, and (3) two out of three reported experimental A factors for methylcyclobutane. An analysis of these and previous results leads to a value of the CHz(lA1) H C H Z (~B J energy splitting of 9 f 3 kcal/mole.

High‐energy kinetic study of chemically activated 1,1‐dichlorocyclopropane

“…The RRKM calculations show that the reacting methylene formed by photolysis of ketene at a wavelength of 277,313, and 334 nm contains a'mean vibrational excess energy of 14 kJ/mol. Similar values have been found by Simons et al [13] and Topor and Carr [31] for the internal energies of CH#A1), which inserts into the C-H bond of cyclobutane and cyclopropane. These two groups have reported a wavelength dependence of E c H~, which in our work probably is present also, but obscured by experimental scatter.…”

“…Furthermore it was important for our calculations that the discussion on the Reaction mechanism of the photolysis of ketene in the presence of heat of formation of CH2(IA1), which received much interest in recent years, was finally settled in favor of the value AHo(CH2,'A1) = 414 f 8 kJ/mol [13][14][15][16].…”

Computationally simple model for multiphoton-induced chemical processes

“…N. Ganapathlsubramanian and Richard M. Noyes* Department of Chemistry, University of Oregon, Eugene, Oregon 97403 (Received: January 28, 1982; In Final Form: April 28,1982) If either Ag+ or Br' is added to an inert supporting electrolyte, the potential of a bromide ion selective electrode is in quantitative (±1 mV) agreement with prediction. Response time of the electrode is usually less than 1 min and often only a few seconds.…”

Intramolecular vibrational energy relaxation. Decomposition of chemically activated alkylcyclobutanes

“…calculations were carried out for the decomposition rates of randomized ethyl cyclobutane (ECB), randomized dimethyl cyclobutane (DMCB), and its corresponding initial MCB moiety.' Calculation for the MCB nascent moiety was based on Simons' model I1 for MCB (20), with minor changes as appropriate. Vibrational frequencies of energized molecules ECB and DMCB were deduced from those of MCB, with necessary extensions and modifications.…”

“…The upper limit is provided by the excess photolysis and vibrational energies carried by methylene (20,25). Based on experimental results for MCB (20), a value of E* = 115.6 kcal mol-' was used.…”